Download climate change and connectivity: are corridors the solution?

CLIMATE CHANGE AND
CONNECTIVITY: ARE CORRIDORS THE
SOLUTION?
Sarah-Taïssir Bencharif (5581063)
613-533-1024
[email protected]
An independent study project submitted to the School of Environmental
Studies in partial fulfillment of the requirements of the Bachelor of
Science (Honours)
Queen’s University
Kingston, Ontario, Canada
April 2010
ABSTRACT
This paper reviews the significance and use of conservation corridors at different geographic
scales (local, regional and continental) as a conservation management tool to mitigate the effects
of climate change on habitat and biodiversity. Species’ habitats are affected by habitat
fragmentation, degradation, and now, climate change. The theory of island biogeography holds
that the number of species within any given habitat patch exists in a dynamic equilibrium
between extinction and colonization. Consequently, a general principle of biodiversity
conservation has emerged stating that practitioners should try and connect habitat patches
wherever possible. Conservation corridors are habitat strips connecting two main patches
together because habitat fragmentation can disrupt natural population dynamics by reducing
species dispersal and even causing local extinctions. Climate change will cause changes to mean
annual temperature, precipitation patterns, the incidences of severe weather events, and the
frequency and intensity of disruption regimes (ex: forest fires). The effects of climate change as
well as habitat degradation and fragmentation will compromise species’ ability to adapt their
habitat ranges to new climate. An analysis of case studies from the peer-reviewed literature
shows that the implementation of corridors at broader scales would best mitigate the effects of
climate change and maintain the integrity of ecosystem processes.
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TABLE OF CONTENTS
ABSTRACT………………………………………………………………………………………1
LIST OF FIGURES……………………………………………….……………………………..3
1.0
INTRODUCTION…………………...…………………………………………………..4
1.1 RESEARCH OBJECTIVES……………………...…………………………………..4
2.0
METHODOLOGY................................................................................................... 5
3.0 BACKGROUND INFORMATION ON CONSERVATION CORRIDORS………........7
3.1 THEIR USES AND SCALE-DEPENDENCY…………….………………....…......7
3.2 ISLAND BIOGEOGRAPHIC THEORY………………………….…………….......9
3.3 IMPACT OF CLIMATE CHANGE ON BIODIVERSITY………………………..11
4.0 LITERATURE REVIEW…………………………………………………………….........13
4.1 LOCAL HEDGEROWS IN AN AGRICULTURAL SETTING…………......13
4.2 LOCAL HEDGEROWS IN WOODLOTS…………………………………...14
4.3 LOCAL FOREST CONSERVATION CORRIDOR…………….……….......15
4.4 LOCAL CORRIDORS AND PLANT DIVERSITY……………………………....17
4.5 REGIONAL CONSERVATION CORRIDOR IN AMAZONIA………………….20
4.6 REGIONAL RIPARIAN CONSERVATION CORRIDOR…………………….…21
4.7 CONTINENTAL YELLOWSTONE-TO-YUKON PROJECT…………………....24
4.8 CONTINENTAL AUSTRALIAN CONSERVATION CORRIDOR……………...26
4.9 TEMPORAL CORRIDORS……………………………………………………..…27
5.0
RECOMMENDATIONS……………………………………………………..………..29
6.0
SUMMARY……………………………………………………………………………..30
7.0
ACKNOWLEDGMENTS ……………………………………………………..…31
8.0
APPENDIX A………………………………………………………………………….32
9.0
APPENDIX B…………………………………………………………………………...33
10.0
REFERENCES………………………………………………………………………...37
2
LIST OF FIGURES
Figure 1: Six sites for study on plant species richness and conservation corridors
Figure 2: Relationship between biodiversity and corridor width
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1.0 INTRODUCTION
1.1 RESEARCH OBJECTIVES
Conservation corridors serve to link patches of habitat together and are either artificially
created through landscape restoration or follow remnant natural landscape features such as
gallery forests and riparian corridors. Their effectiveness in increasing connectivity has been
both supported and contested. While some studies show that corridors do in fact facilitate
dispersal by increasing immigration and emigration rates and effectively improve gene flow from
one habitat patch to another, other studies conclude that they can also act as conduits for the
spread of diseases, exotic species, and disturbances, such as floods and wildfires (see review in
Beier and Noss 1998). The efficacy of conservation corridors is important to consider since
habitat loss and degradation is currently one of the main threats to biodiversity.
Species’ habitats face two primary sources of stress, both anthropogenic in nature: habitat
loss (or the related process of habitat fragmentation) and climate change. The goal of this project
is to establish the significance and use of conservation corridors of different types and at
different scales as a tool for responsive conservation management under the continued threat of
climate change. These goals are achieved by accomplishing the following steps:
1. Defining the types of corridors that have been used based on both their habitat and
their scale
2. Using the forecasted climate change-induced habitat losses and threats
3. Establishing the characteristics of both the corridor and the surrounding matrix
which can affect the effectiveness of a corridor. This is done by assessing changes
in a certain targeted biological property, including genetic drift, re-colonization
after a habitat disturbance or local extinction, and migration. The characteristics
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used to define the applicability of a corridor were compiled from the available
literature either in the form of explicit tables or as described variables in the
study.
4. Determining the effects of the selected species on the studies’ results
5. Examining some of the current policies regarding habitat management in light of
climate change and determining their relevance based on the conclusions found
here regarding the type and the scale of the corridor.
2.0 METHODOLOGY
All research was supported by a thorough literature review of peer-reviewed scientific
articles and books. The majority of the literature used in this paper was published within the last
ten years, ensuring that the most recent findings were reported. This project’s scope was limited
to the available, published data in peer-reviewed journals and in books, as well as by the fact that
many of the studies are not replicable due to their scale.
In selecting the studies to be examined in this report, it was important to choose a variety
of conservation corridor types: there needed to be a variety of habitats, of focus species or
taxonomic groups, and of matrices. Consequently, this report features recent studies that
examined the role of conservation corridors in rainforests, rainforests along rivers (riparian),
agricultural systems, montane habitats, and coniferous forests for example (see Appendix B).
While some studies focused on the use of conservation corridors by a single species or taxon,
others examined the role of conservation corridors across multiple taxa. As such, this report
presents results relevant to avian species, plant communities, insects, amphibians, and mammals,
from rodents to top carnivores.
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The studies examined were selected because of their diversity of systems but also
because they present an assortment of climate-change and anthropogenic threats. These direct
anthropogenic habitat loss and fragmentation threats include the intrusion of cattle from adjacent
ranches and the intensity of farming systems. As a result, all of these systems are facing two
pressures: habitat loss and degradation from the above threats as well as rapid climatic changes
which affect habitat quality. Studies reflecting different scales were selected in order to examine
the relationship between habitat preservation and connectivity and climate change. The studies
are considered in light of current and ongoing climatic changes like rising temperatures and an
increased fluctuation in weather patterns. The chosen studies examine the different roles of
corridors: immigration, movement, prevention of genetic drift, and reducing the effects of
demographic stochasticity.
Studying conservation corridors immediately implies that the habitat is, in some way,
fragmented. But it was further important to study fragmented systems experiencing land-use
threats and climate change threats because there is a very close relationship between these two
pressures. “For example, a doubling of CO2 concentration can lead to a production increase of
15-50%, depending on crop and weather conditions, which would have major effects on the area
needed for farming” (Opdam and Wascher 2004). As such, it is critical to study the effects of
climate change on current habitat networks and examine the importance of preserving and
improving habitat connectivity by way of conservation corridors.
Defining the characteristic features of each scale fell into one of two categories: either
determining the physical dimensions that would define each scale, or defining each scale by the
ecological functions and processes it protects. Giving each scale physical dimensions in meters
or kilometers was too arbitrary for this project, although practitioners may find it useful to have
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scale dimensions for different ecosystems. A thorough literature review supported the idea that
processes are scale-dependent and as such, each scale was defined in terms of its level of
connectivity to another corridor system.
The effectiveness of the conservation corridor was evaluated based on two factors: the
study’s reported values on the measured feature (genetic drift, number of species, reported usage
by a species, mortality in the matrix vs. mortality in the corridor), and through a critical
examination of the corridor system’s resilience in the face of climate change.
3.0 BACKGROUND INFORMATION ON CONSERVATION CORRIDORS
3.1 THEIR USES AND SCALE-DEPENDENCY
Different types of corridors characterize the connectivity of the landscape and at different
scales (local, regional, and continental). Conservation corridors can be defined as a “linear, twodimensional landscape element that connects two or more patches of wildlife (animal) habitat
that have been connected in historical time” (Soule and Gilpin 1991). They are surrounded by a
matrix of degraded, mostly unsuitable habitat. The scale of a conservation corridor system is
defined by the ecosystem processes it preserves. For example, a local conservation corridor
which connects a woodlot to another woodlot with a river allows for the preservation of that river
system. A regional corridor system would include the majority of the watershed or many
interconnected local corridors, while a continental conservation corridor would connect the
watershed to either another watershed or another regional scale corridor system. “Functional
connectivity is a scale-dependent feature that depends on the spatial scale at which individuals
perceive and interact with landscape structure by dispersal” (Steffan-Dewenter et al. 2002).
Because each species perceives connectivity in relation to its own characteristics (size, dispersal
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patterns, etc.), it is difficult to define scales with respect to a single species: what may be a
movement corridor to one species may include the full habitat range of another. As such, it is
important to recognize the role of processes in addition to the scale at which they operate.
For example, soil quality is integral to habitat quality. The scale at which soil
decomposers can colonize new habitat patches is a function of the scale of the corridor system:
small and distant patches are less successfully colonized than larger, closer patches (Rantalainen
et al. 2005). Since soil quality is such a vital component of habitat quality and in turn the
maintenance of biodiversity, it is important that the scale at which these processes operate is
understood and taken into account when designing conservation corridor systems (Rantalainen et
al. 2005). This approach recognizes the importance of the preservation of ecosystem functions
and processes as well as the interconnections at all scales: the local conservation corridor is at its
strongest when it is part of a broader network of habitat connectivity (see Appendix A). This
nested design approach strengthens the value of conservation corridors at all scales and provides
the strongest resilience in the face of climate change because it best preserves connectivity
between the most habitat types.
For biodiversity, conservation corridors have four primary reasons to exist (Simberloff et
al. 1992):
1. To increase the rate of species immigration rates by connecting one habitat patch to
another and allowing for the movement of individuals
2. To provide movement routes for species with large home ranges whose habitat is
otherwise completely fragmented, for daily foraging for resources, for seasonal
relocation, and for the dispersal of individuals
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3. To decrease inbreeding depression by increasing the number of individuals in a species,
and
4. To reduce demographic stochasticity: should an event (e.g. disease) jeopardize a
population
3.2 ISLAND BIOGEOGRAPHY THEORY
The study of the interactions between and within discrete habitat patches embedded in a
different matrix allows scientists to better understand the impact of connectivity on species
distribution and ecosystem health. Like islands, habitat patches are surrounded by a different
matrix. Island biogeography theory states that the number of species within any given patch
exists in a dynamic equilibrium between extinction and immigration. Individuals from a species
can migrate to and from a habitat patch using conservation corridors as a conduit for this
movement. Consequently, a general principle of biodiversity conservation has emerged stating
that practitioners should try and connect habitat patches wherever possible to accomplish the
four functions of conservation corridors: to increase immigration, to prevent genetic inbreeding,
to increase movement across fragmented home ranges, and to prevent demographic stochasticity.
A great deal of attention and effort has been placed on implementing this principal into
conservation programs at local, regional and continental scales by way of conservation corridors.
Habitat fragmentation can disrupt natural population dynamics by reducing species
dispersal and even causing local extinctions. The species’ characteristics put them at different
levels of vulnerability to extinction (Purvis et al. 2000):
1. Small populations are at a higher risk than large populations. Habitat loss and degradation
combined with the effects of climate change exacerbates population declines by reducing
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the availability of suitable habitat. Moreover, inbreeding and low population densities
also make small populations more vulnerable to extinction.
2. Highly endemic and specialized species are at a higher risk of extinction because they are
so adapted and specialized for a particular habitat that they cannot migrate and adapt to a
new habitat or set of climatic conditions. They have likely evolved in isolation from other
predators and competitors and so they are very susceptible to extinction in the face of
newly introduced species. Furthermore, they likely have small habitat ranges and small
populations.
3. Species higher on the food chain are more vulnerable to extinction as they depend on
other species’ survival (chains of extinction) and often have larger home ranges. This has
great significance in the analysis of studies about corridor use since the chosen specie’s
use of a corridor is a factor of its trophic level.
4. K-selected specialists living in habitat patches are more vulnerable to extinction because
they produce fewer offspring that take longer to reach maturity. This means that they are
less able to compensate for increased mortality with increased fecundity, increasing their
vulnerability to extinction.
5. Highly social species with complex mating and foraging social structures are at risk
because survival of individuals depends on the survival of the group.
6. Species with a large habitat range are especially vulnerable to habitat degradation and
loss because their fragmented habitat exposes them significantly to the negative impacts
of edge effects. Being bigger and more visible, they are also more likely to roam in the
matrix, further exposing them to hunting.
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7. Species that have a large body size are more susceptible to extinction because they tend
to be K-selected specialists, have large home ranges, low population densities, and are
more vulnerable to hunting.
8. Diurnal species are vulnerable because they display many of the above species: they are
social, they have large home ranges, and have large body sizes.
In assessing the conservation role of corridors in mitigating the extinction of species, it is
important to consider the focal species in the study and whether it is especially prone to
extinction as based on the above criteria.
3.3 THE IMPACT OF CLIMATE CHANGE ON BIODIVERSITY
The impact of global climate change on biodiversity is complex. The rise in greenhouse
gas emissions has caused global temperatures to change, affecting regional precipitation patterns,
and causing changes in disturbance regimes, including in the length and intensity of forest fires
(Opdam and Wascher 2004). Extensive habitat fragmentation, changes to disturbance regimes,
habitat destruction and degradation from anthropogenic sources and global climate change
complicate habitat and species management plans. Flexible, multi-scenario management plans
must be created in order to address the needs of an ever-changing climate and habitat.
Global climate change will impact habitat by causing the loss of colder climate habitats
and by increasing the incidence of intense weather events such as droughts and coastal floods
(Opdam and Wascher 2004). One of the anticipated climate change scenarios describes a
situation where habitats with the most altitudinal gradient could ideally provide the most
adaptability to climate change, allowing for the “linear migration of all remaining habitats
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upslope” (Halpin 1997). However, even the “top habitat” has its limits and most habitats do not
even have an altitudinal gradient. Conservation managers must develop creative methods to
maintain the integrity of the habitat-species relationship, in particular for habitat specialists who
are most likely to be locally extirpated or globally extinct as their distinct habitat characteristics
are jeopardized.
Even local reforestation initiatives cannot completely recreate a desired habitat for a
species in a timely way. The red-backed vole (Clethrionomys gapperi), a habitat specialist
preferring closed-canopy old growth forests lives side-by-side with the deer mouse (Peromyscus
maniculatus), a habitat generalist, in a more limited closed-canopy forest area despite there being
nearby newer growth forests (Mech and Hallett 2000).
A species’ ability to cope with habitat loss and degradation due to climate change is
influenced by a number of factors (Halpin 1997), including:
1. the rate of climate change as influenced by anthropogenic greenhouse gas emissions and
land use changes
2. the species’ ability to migrate to more suitable habitat as dictated by its habitat range,
habitat connectivity, and the actual mobility of the species (ex: plants that are wind vs.
animal dispersed)
3. the biological competition between co-existing species: generalists and specialists adapt
differently to habitat loss and degradation, since generalists may be able to better utilize
resources and survive in the degraded habitat than specialists
4. changes in the ecosystem’s disturbance regime (ex: the length and intensity of a forest
fire may impact the suitability of a habitat for a species)
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5. physical barriers to migration and use of suitable habitat: an unsuitable matrix which
increases their risk of predation, urban development and sprawl which fragments a
habitat
In general, individual members of species respond to changing habitats and climates by
adapting their habitat range to the stress(es) in question, be it climate change, fragmentation, or
both (Lyons 2003). The reconstruction of past ecosystem community structures has shown that
communities are highly variable and can very often present non-analog scenarios, or perhaps it is
that modern ecological communities have no past analogs. Late Pleistocene and late Holocene
mammal assemblages show that in response to receding glaciers, certain species (montane vole
(Microtus montanus) and eastern chipmunk (Tamias striatus)) migrated gradually westward
following the changing precipitation pattern along a moisture gradient. Other species like the
southern bog lemming (Synaptomys cooperi) shifted their habitat range north as the glaciers
receded (FAUNMAP Working Group 1996). However, as modern ecological communities have
no historical analog, it remains difficult to predict how specific communities will change.
4.0 LITERATURE REVIEW
4.1 LOCAL HEDGEROWS IN AN AGRICULTURAL SETTING
Hedgerows are narrow corridors of shrubs, trees, and bushes that have often been used in
agricultural landscapes either as barriers between agricultural patches or, in the context of
connectivity, to connect one non-agricultural patch of habitat with another. In examining the use
and impact of connective corridors at the hedgerow scale in agricultural settings, Baudry et al.
(2003) determined that modes of agricultural production actually affect the use of hedgerow
corridors. They compared two farm land types with similar landscape connectivity patterns but
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which housed different farming systems. The two farming systems differed in their level of
farming intensity, with one having more permanent grasslands and hedgerows and the other
more maize. Baudry et al. (2003) rejected the “suitable habitat” and “unsuitable matrix”
dichotomy because in an agricultural setting, the “unsuitable matrix” can often be used as a
corridor in and of itself, almost simulating a temporarily suitable habitat. For certain insect
species, maize fields can give the same traveling protection as forests (Baudry et al. 2003).
The study shows that while hedgerows are somewhat important at the local scale, their
effectiveness is heavily affected by small changes in farming practice, like the distribution or
rotation of crops. If hedgerows, as an isolated system, barely offer any connective resilience in
the face of these very small-scale changes, it is difficult to foresee their usefulness in light of the
global scale climate changes.
4.2 LOCAL HEDGEROWS IN WOODLOTS
The effectiveness of hedgerows in the face of climate change was also studied in the
context of a woodland habitat (Davies and Pullin 2007). Hedgerow connective corridors in
woodland habitat have been criticized because they produce significant edge effects, exposing
the species that use them to edge predation. Davies and Pullin (2007) conducted a literature
review about hedgerows in various forest systems. They classified their results by taxonomic
group. Their results indicate that for mammals (mostly rodents), hedgerows did increase the
dispersal rate of individuals between woods. In the case of birds, hedgerows were used by
smaller birds, but larger birds tended to fly directly from one woodlot to another. This is, of
course, limited by the proximity of one woodlot to the next. The invertebrate study species of
choice are the carabid beetles (of the beetle family Carabidae) because they are sensitive to forest
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fragmentation (Oates et al. 2005). Moreover, the many species of carabid beetles respond
differently to forest fragmentation and degradation. The larger, specialist species of carabid
beetles don’t tend to disperse as much as the smaller, generalist species whose populations were
found to increase as forests become more fragmented (Oates et al. 2005). Overall, there was a
direct relationship between habitat connectivity and mortality: beetles, big or small, that traveled
across the habitat matrix had a much higher mortality (Davies and Pullin 2007). Amphibians
used hedgerow corridors as connective habitat between the two habitats they need in their life
cycles, namely land and water. Davies and Pullin (2007) note, however, that none of the studies
so far adequately assess the long-term viability of hedgerow corridors, in particular while facing
climate change. However, if hedgerows are considered as habitat in themselves, as they are for
nesting and roosting birds, and many rodents, their preservation remains important as long as
they are part of a broader network of connectivity.
Climate change will change species’ habitat range. Ideally, conservation corridors
provide a conduit to more suitable climate and habitat. Climate functions at a much bigger scale
than the hedgerow. Given the limited resources allocated to conservation management, it is
perhaps best to allocate the majority of them to conservation management plans at larger scales.
Hedgerows cannot be dismissed as a conservation tool as long as they are integrated as part of a
larger scale network of habitat connectivity.
4.3 LOCAL FOREST CONSERVATION CORRIDOR
A forest corridor is a linear corridor composed of the same forest type as the two forest
habitat patches it connects. Forest corridors have lately been developed as part of an adaptive
15
forest management strategy whereby forest patches and corridors are left unlogged to study the
effectiveness of corridors in mitigating loss of biodiversity (Mech and Hallett 2000).
At the local level, the effectiveness of forest corridors has been examined through a
genetic approach. The Pend Oreille River drainage located in northeastern Washington has a
coniferous forest which includes Douglas fir (Pseudotsuga menziesii), grand fir (Abies grandis),
western hemlock (Tsuga heterophylla), western larch (Larix occidentalis), lodgepole pine (Pinus
contorta), and western red cedar (Thuja plicata). This coniferous forest has a diverse
combination of old growth, new growth, clear cut, and regenerated forest areas. Mech and Hallett
(2000) undertook their study using linear forest corridors that were less than 150 meters wide
that directly link two forest patches. They chose two study species: the red-backed vole
(Clethrionomys gapperi) and the deer mouse (Peromyscus maniculatus). These two species
differ most significantly in their preferred habitat: the deer mouse (P. maniculatus), as a habitat
generalist, can live in both old growth and new growth forests, while the red-backed vole (C.
gapperi) prefers mature forest cover. The habitat matrix analysis used two unseparated sites in
the same large patch as a control system for genetic change, and identified unconnected sites
with which to also compare the results from the corridor networks. By examining the genetic
differences between fully connected, isolated, and corridor-bridged landscapes, the usefulness of
corridors in this ecosystem was determined. In the case of the red-backed vole (C. gapperi), the
genetic distance in isolated sites was significantly higher (0.59 +/- 0.18) than that of the vole
populations in contiguous forest sites (0.19 +/- 0.01), with the populations living in corridorconnected sites being between the two (0.41 +/- 0.11), indicating that the corridors improved
gene flow for this species. In the case of the deer mouse (P. maniculatus), however, there was no
significant difference between any of the landscape types, and Mech and Hallett (2000) attribute
16
this to the deer mouse (P. maniculatus) being a habitat generalist that can thrive in the clear cut
forest matrix.
The width of the corridor itself likely affected the results found for the red-backed vole
(C. gapperi). As all corridors were less than 150 meters wide (100 m wide, on average), the edge
effects likely limited the suitable habitat within the corridor itself and therefore somewhat
limited the population’s movements and the associated gene flow (Mech and Hallett 2000). Their
study indicates that conservation corridors are very useful in promoting gene flow for habitat
specialists but are less critical to populations of habitat generalists.
In light of climate change’s effects on habitat availability and suitability, this will have an
important impact on the differential survival of generalist and specialist species.
Local corridors will also be important in avoiding local extirpation of species. This is
particularly true for species requiring more than one habitat in their life cycle, as is the case with
amphibians. They may require corridors to connect them to their aquatic and land habitats
(Rosenberg, Noon and Meslow 1997).
4.4 LOCAL CORRIDORS AND PLANT DIVERSITY
Henein and Merriam (1990) aptly demonstrated that the quality of the habitat affects the
conservation of populations. If a local scale corridor is set-up but is of low quality, and if it
connects a new habitat patch to a network, the low quality corridor will reduce the survival
probability of its users and it will create a population sink by reducing the population’s size
(Fahrig and Merriam 1994). Conservation corridors at the local scale suffer most from edge
effects and so implementing low quality corridors at those scales may ultimately be detrimental
to population size.
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While most studies focus on the use of corridors by animal species, their survival
ultimately depends on their habitat quality. This is largely affected by the distribution of suitable
plant species. Damschen et al. (2006) examined the long-term role of corridors in plant species
richness. Their study provides a broader ecosystem study on the use of corridors. They created
six study landscapes to replicate their study. Each included a 100 meters by 100 meters central
patch surrounded by four other patches 150 meters away. One of these four patches was
connected to the central patch by a 150 meter by 25 meter corridor. The unconnected patches had
the same total area as the central patch and its corridor. The unconnected patches were of two
different types: winged or rectangular. They had the same edge-to-area ratio (Figure 1.0). The
patches consisted of open habitat with young longleaf pines (Pinus palustris) while the
surrounding forest was a dense pine forest. The number of species in connected and unconnected
patches was the same when the landscapes were created. However, at the end of five years, their
results show that the connected patches had 20% more plant species than the unconnected ones.
Their results also show that given an equal edge-to-area ratio, patch shape does not affect plant
species richness. This study strongly supports the use of local corridors in maintaining plant
species richness (Damschen et al. 2006). Ultimately this plant species richness strongly
determines the quality of the habitat itself.
In the last 10,000 years, vegetation communities have changed in response to climate
change and they will most continue to do so in the face of added anthropogenic climate change.
This study is a good indication that we must continue to mitigate the loss of connected
landscapes and to restore connectivity because their plant community richness is significantly
higher than in disconnected landscapes. Protecting habitat is at the root of protecting
biodiversity, and connectivity provides a great advantage to the protection of biodiversity.
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Figure 1.0 (Taken from Damschen et al.2006) This is one of the six study sites
created to examine the role of conservation corridors in plant species richness.
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4.5 REGIONAL CONSERVATION CORRIDOR IN AMAZONIA
The Amazon Rainforest is one of the world’s most biodiverse regions and is experiencing
very rapid forest fragmentation and deforestation (Laurance and Williamson 2001). The forest
has been deforested for agricultural production, cattle ranching, logging, and for fuel wood
(Laurance and Williamson 2001). Deforestation reduces plant evapotranspiration, thereby
limiting regional rainfall, which increases the incidence of forest fires (Laurance and Williamson
2001). Furthermore, cattle pastures are regularly burned all the way to the forest’s edges which
already have drier trees, making them even more susceptible to forest fires, especially with the
warmer, drier climate caused by global climate change (Laurance and Williamson 2001).
Whether corridors in this tropical rainforest could help mitigate biodiversity loss is an important
question as this forest is a critical carbon sink in a world with increasing carbon dioxide
emissions (Laurance and Williamson 2001). “Protected area systems and conservation corridors
can help mitigate the impacts of climate change on Amazonian biodiversity” (Killeen and
Solorzano 2008). While most studies concerned use an animal species to assess the usefulness of
corridors, Killeen and Solorzano (2008) examine a central feature of the Amazon rainforest: its
precipitation regime. The precipitation regime is central to the biodiversity of the rainforest, and
it is strongly affected by the available forest land cover. As such, it is important to examine how
different corridors will impact this regime and in turn biodiversity. Killeen and Solorzano (2008)
promote the use of conservation corridors with a buffer ecotone all along the edges of the
corridor. An ecotone is a transitional habitat between two ecosystem types and thus contains a
multitude of habitat types (Killeen and Solorzano 2008). These conservation corridors should
“span environmental gradients to ensure that species can shift range distributions” (Killeen and
Solorzano 2008).
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They add that some species may have the genetic plasticity to adapt to climate change
and continue to live in the habitat gradient provided by the corridor. However, they do not
provide a timeframe for this genetic plasticity or specify which species are most and least likely
to suffer in these corridor gradients over time. As an example of a corridor gradient, they propose
an altitudinal corridor, ranging from lowland forest to higher montane habitat as a single,
uninterrupted corridor. This allows the conservation of the full range of species in the different
ecosystems while allowing for possible displacements as an adaptation to the effects of climate
change, as on the precipitation regime (Killeen and Solorzano 2008). But where do the species
living at the top go?
4.6 REGIONAL RIPARIAN CONSERVATION CORRIDOR
Riparian corridors are strips of habitat that follow rivers and forest streams. Their
protection could be advantageous because it encompasses aquatic, land and aerial habitat for
many species, making it a hot spot for conservation potential. Riparian habitats are highly
sensitive to the effects of climate change because they are heavily reliant on macroclimatic
cycles and regimes (ex: precipitation cycle) that are affected by anthropogenic climate change.
Moreover, while the development of other corridor types (ex: forest) focuses more on their value
in species dispersal, riparian corridors must also be examined as the actual home range of many
endemic and non-endemic species.
To assess the conservation value of riparian corridors, Lees and Peres (2007) conducted a
study using 37 riparian sites in the heterogeneous, fragmented Amazon forest of Brazil. They
compared their results from connected riparian sites, riparian patches separated by at least 300
meters from the closest forest patch, and control sites in large, undisturbed forested areas. Their
21
selected indicator species included avian species (except waterbirds, nocturnal birds, and aerial
insectivores) and mammal species (diurnal primates, ungulates, carnivores, large rodents,
armadillos), making their results especially useful in assessing the effectiveness of riparian
corridors across taxa. The study’s focus was on the corridor width that best preserved the
biodiversity assemblage and the canopy structure of the Amazon. Logging companies are
required by Brazilian federal legislation to leave intact riparian forest strips of various widths
along rivers. In this legislation, the corridor’s width is based on the river’s width (Lees and Peres
2007).
Their results show that the use of corridors by birds is species-specific. For example, the
availability of palm (Mauritia flexuosa) in unconnected corridors affected the distribution of the
red-bellied macaw. This species was found to be present in both connected and unconnected
areas but was more abundant in palm-rich unconnected areas (Lees and Peres 2007). Their study
also described the quality of the habitat based on the amount of canopy cover, how fragmented it
is, and how affected it is by local cattle intrusions. Their results show that sensitive species only
thrive in high quality habitat while less sensitive species can be found in fragmented, lower
quality habitat (Lees and Peres 2007). If the results are interpreted in light of biodiversity, it
becomes clear that unconnected riparian corridors and narrow, connected riparian corridors have
fewer species than the wider, connected riparian corridors and the undisturbed control riparian
habitats (Lees and Peres 2007).
22
Figure 2.0 (taken from Lees and Peres, 2007): The relationship between the number of
avian species (a, b) and mammal species (c, d) in relation to corridor width and forest
habitat quality (the shaded circle is connected habitat, the open triangle is the unconnected
habitat, and the dark squares are the continuous forest areas).
In the case of mammalian diversity, the response is also species-specific. While some
species, like the spider monkey [Ateles sp.], were not found at all in corridors, many other
species were found to use riparian corridors as habitat or for migration from one area to another.
Lees and Peres (2007) show that corridor width is a primary indicator of riparian corridor
success. Narrow riparian corridors fail to preserve the “intact canopy structure” required for
effective biodiversity management (Lees and Peres 2007). A narrow corridor is less than 200
meters wide and is much more susceptible to edge effects. There is a plateau in the increase in
biodiversity once a corridor reaches 400 meters in width and can actually consist primarily of
interior habitat (Figure 2.0). This study shows how riparian corridors can benefit from increasing
their width to avoid species overcrowding and to mitigate edge effects. Wider riparian corridors
also allow for a larger range of heterogeneous microhabitats, thereby increasing species diversity
and allowing sensitive species to thrive (Lees and Peres 2007). Current forest management
23
practices in the Brazilian Amazon do not conserve biodiversity because the width requirements
are seriously inadequate. For example, the minimum corridor width is 30 meters for rivers or
streams less than 10 meters wide (Lees and Peres 2007).
The narrow corridors being implemented provide less protection from erosion, cattle
intrusions and edge effects than is required. Changes in climatic patterns will require larger
corridors to provide more heterogenous microhabitats and dispersal routes for species at different
trophic levels. In the case of carnivores, wider corridors can serve as a movement route to better
habitat, and in the case of insect populations or small rodents where the corridor acts as a habitat
itself, a wider and more protective corridor can provide multiple microhabitats and better
protection from edge predation.
4.7 CONTINENTAL YELLOWSTONE-TO-YUKON PROJECT
At the continental scale, it can be very difficult to preserve large habitats. This is
arguably the most important scale at which connectivity must operate because it provides a much
more diverse set of habitats to which species can migrate and adapt when facing climatic
changes. Moreover, preserving natural ecosystems provides a certain regulatory system on the
climate itself. In North America, there are three primary climate drivers. First, global circulation
patterns and other broad drivers like solar insolation affect climatic averages. Second, patterns
like the Northern Annular Mode (NAM), the Pacific-North American pattern (PNA) and the El
Nino-Southern Oscillation (ENSO) regulate climate. Third, “mesoscale” topographic features
affect weather patterns (Peters et al. 2008). Terrestrial ecosystems strongly affect climate
through biophysical and biogeochemical processes, whereby land cover changes affect the
energy balance, for example (Peters et al. 2008).
24
The Yellowstone-to-Yukon Project seeks to connect northern Canada and the Greater
Yellowstone Ecosystem. It encompasses 1.2 million square kilometers of habitat. In 1991,
researchers tagged a five-year-old female gray wolf (Canis lupus) with a radio collar and satellite
transmitter to determine her home range. Over two years, she travelled over 100 000 square
kilometers including over the mountains (y2y.net). The use of large carnivores is often important
in determining what habitats are preserved: by protecting the habitat range of large carnivores, it
inevitably encompasses that of species with smaller home ranges. However, the Yellowstone to
Yukon area is still facing threats from roads and railways which continue to fragment the habitat.
Roads continue to fragment habitat and to kill animals in wildlife-vehicle collisions. In
response to this, overpasses and underpasses are created to create safe ways for animals to cross
the existing highways and roads, as with the Highway 206 underpass. Underpasses are tunnels
built under roads and overpasses are bridges built above the roads. Both are used to provide a
safe route across the road fragmenting the habitat.
The available peer-reviewed literature on this corridor at the continental scale is limited
because studies focus on the regional and local scale corridors nested within this continental
scale.
At the continental scale, the Yellowstone to Yukon project is the most effective in
mitigating the impact of climate change on species by providing them with more extensive
habitat to which they can migrate and adapt. It is important to note that this project includes
mountain ranges which allow for an altitudinal gradient to which species can migrate. The
importance of continental scale corridors as well as their limitations are highlighted by the
changes already experienced by many species in the region (Blatter and Ingram 2001).
25
The North American red squirrel (Tamiasciurus hudsonicus) now reproduces earlier
because of the earlier springs which provide them with an earlier supply of spruce cones
(Bradshaw and Holzapfel 2006). In the case of the grizzly bears (Ursus arctos horribilis), the
warmer, earlier summers mean that the blister rust, Cronartium ribicola, which devastates the
whitebark pine trees (Pinus albicaulis) can do so for longer periods of time (Schneider and Root
2002). The whitebark pine seeds (P. albicaulis) are critical to the bears’ diet. These longer
summers threaten the bears’ food source, but if the preserved habitat is large, the grizzly bears
can potentially shift their diet or range to find enough food (Schneider and Root 2002). It is
critical that we maintain connectivity of habitat so that species can adapt in the face of climatic
pressures like the ones described above.
The altitudinal gradient provided by the protected mountain ranges helps maintain
America pika (Ochatona princeps) populations. Pikas (O. princeps) are alpine lagomorphs which
eat grasses, lichens and shrubs that grow between rocks on mountains. Their food sources are
responding to climatic changes by shifting their ranges to the mountainsides and by growing
earlier in the year. In response to this, pika (O. princeps) are following their food source but are
also separated from each other, limiting their ability to meet and breed. Their populations are
already in decline and their upward migration is fragmenting their populations (y2y.net).
The scale of the Yellowstone to Yukon project allows for species to migrate and adapt
when facing climatic changes and is the best scale at which conservation efforts should operate.
4.8 CONTINENTAL AUSTRALIAN CONSERVATION CORRIDOR
The conservation potential afforded by continental-scale conservation corridors are also
highlighted in the implementation of the Australian Alps conservation corridor. This
26
conservation corridor spans north-south along the Great Dividing Range’s watershed in
Australia. It is a 690km long corridor encompassing 1,657,570 hectares of continuous habitat.
There are currently gaps in the conservation corridor in the upper Jamberoo Valley, for example.
“Land clearing [is] the single greatest threat to Australian terrestrial biodiversity” (Pulsford et al.
2003). Implementing and connecting this conservation corridor would connect a coastal habitat
with an alpine area, providing a stronger connectivity network for the Australian moist eucalypt
forests (Pulsford et al. 2003).
4.9 TEMPORAL CORRIDORS
Going beyond the traditionally geographic definition of a corridor, the temporal corridor
accounts for the climate regime of the area using climate models to enhance conservation
planning. Anticipated global climate change should indeed be accounted for in the development
of physical corridors (Rose and Burton 2009). If the climate changes so much so that the
physical corridors themselves do not give a sufficient chance of survival and adaptability to the
species, then an alternate conservation planning method must be created that does account for the
future change. As in the case of corridors in the Amazon which account for the precipitation
regime, further studies should be conducted to examine the longer-term potential of corridors in
supporting biodiversity in a changing climate. It is thus important that the study of corridors be
“coupled with process-based models for a more refined projection of climate change impacts on
biodiversity” (Rose and Burton 2009). Temporal corridors are maps of a climatic feature’s
current range and distribution and they present its changes through time using models. This
feature of the temporal corridor is especially useful for habitat specialists—as climate and habitat
type are intrinsically linked—as well as for migrating species which will need new migration
27
refugia as the changing climate alters their available habitat through extended forest fires, for
example.
The use of temporal corridors strengthens conservation planning because it allows for the
implementation of conservation corridors in such a way that they maintain the ecosystem’s basic
functions and features according to where they will be in the future. Temporal corridors are
limited, however, by the fact that there are many climatic scenarios available. Furthermore, these
climatic models are constantly changing since climate predictions are affected by our current
anthropogenic greenhouse gas emissions.
28
5.0 RECOMMENDATIONS
Based on the previous analysis of conservation corridors at three geographic
scales (local, regional, continental), the following recommendations emerge to strengthen
the implementation of corridors in light of global climatic changes:
1. Corridors should preserve the integrity of the ecosystem’s functions at all scales.
2. Conservation corridor networks must be connected at all scales to improve the resilience
of biodiversity in the face of climate change.
3. Conservation management plans should make good use of models on anticipated climatic
regimes to preserve ecological functions based on future climatic patterns, as altered by
global climate change.
4. Further emphasis should be placed on the implementation of broader, continental scale
conservation corridor networks. This can be done by connecting the current local and
regional conservation corridors to one another to enhance their effectiveness and
resilience in the face of climatic changes.
5. We should continue investing our reforestation efforts as a buffer area around the current
corridors and patches as a means of more quickly rendering what was previously an edge
into an actual, suitable habitat. This is a good transition for the corridor strip from its role
as a movement corridor to a full habitat. Since it takes decades, even centuries, for newly
planted forests to develop the ecosystem functions of older forests, and since they are
more likely to be inhabited by habitat generalists for a long time, it may be a better use of
our time and resources to reforest the areas directly around forest patches and their
connective corridors.
29
6. It is imperative that governing bodies come to agreements on ways to curb anthropogenic
greenhouse gas emissions to reduce the impacts of climate change in the years to come.
The inconclusive summit held in Copenhagen in 2009 is a reminder that we must
continue to push for a reduction of our ecological footprint.
6.0 SUMMARY
This paper reviewed the use of conservation corridors in fragmented landscapes at
three different scales to investigate their effectiveness in mitigating the effects of climate
change on habitat and biodiversity. An analysis of studies performed at the different
scales show s that the implementation of conservation corridors at the broadest scales
would best mitigate the effects of climate change while preserving ecosystem processes.
The following is a summary of the conclusions drawn in this paper.
1. Climate change already strongly impacts species ecology (Schneider and Root 2002).
2. Ecological processes are scale-dependent (Steffan-Dewenter et al. 2002).
3. The intensity of habitat degradation in the matrix affects the use of corridors by species
and the matrix itself can be used as habitat by some species (Baudry et al. 2003)
4. Plant species richness, and in turn habitat quality, is significantly improved at the local by
connectivity starting at the local scale (Damschen et al. 2000).
5. Species characteristics play a major role in their adaptability to climate change (Halpin
1997) and in their vulnerability to extinction (Purvis et al. 2000).
6. Local conservation corridors improve the genetic diversity of specialists more so than for
generalists (Mech and Hallett 2000).
30
7. Forest corridors 100-150 meters wide suffer significant edge effects. Whenever possible,
we should make them wider than 150 meters to increase the size of utilizable interior
habitat , especially for specialists (Mech and Hallett 2000).
8. Riparian corridors should aim to be 400 meters in width to preserve intact core habitats,
canopy structure and biodiversity (Lees and Peres 2007).
9. Connective corridors should be aligned upslope, from the coast to the mainland, and
poleward in order to conserve the most habitat types and ease the movement of species as
the climate changes (Noss 1992). The question remains: what about the species in the top
habitat?
10. Local and regional conservation corridors can best mitigate the impacts of climate change
on biodiversity when they are included as part of a broader habitat connectivity network.
11. The nested conservation corridor approach recognizes that continental scale corridors are
made up of regional corridor systems which are in turn made up of local scale corridors.
12. With global climate change underway, we must recognize that we will see many nonanalog vegetation and animal communities. As such, we have to leave enough flexibility
in our management plans for these inevitable ecological changes.
13. We must continue to develop and use more localized temporal corridors to strengthen
conservation planning.
7.0 ACKNOWLEDGMENTS
I would like to thank Dr. Ryan Danby for providing me with invaluable suggestions,
guidance and encouragement in this project and Dr. Graham Whitelaw for being my second
reader. I would also like to thank Dr. Louise Winn for coordinating this course.
31
8.0 APPENDIX A
This diagram illustrates the nested design approach applied to conservation corridor scales.
It emphasizes the importance of developing a broader network of connectivity comprised of local
and regional scale corridors to make up a continental system of habitat connectivity.
32
9.0 APPENDIX B: SUMMARY TABLE
This summary table was based on the one provided by Beier and Noss (1998). The case studies in section 4.0 of this paper
were summarized in this table. It is important to include the taxonomic group on which each study focused because the results
indicate that conservation corridor use can be species-specific. The utility of the conservation corridor was assessed in light of
climate change and the scale at which it operates.
Study
Country/Region
Scale
Taxonomic
Group(s) and
Study Species
Matrix
Baudry et al.
2003
France
Local
Invertebrate:
forest carabid
species
Agricultural
land
Davies and
Pullin, 2007
(review)
Multiple
Local
Mammals,
birds,
amphibians,
invertebrates
Rodents, many
birds, carabid
Arable and
pastoral lands
33
Type of
Study System
Study
(Sampling
effort)
Simulations
Farms with
and
small woodlots
previously
radio-traced
forest species
(seven year
crop
succession on
17 farms)
Literature
review of
hedgerow
effectiveness
(27 studies)
Woodland
Utility of corridor
Agricultural land use
management strongly
impacts utility of
hedgerows but their
implementation should be
done in conjunction with
managing the intensity of
the farming done in the
matrix. Seeing as they are
sensitive to changes in
agricultural intensity, they
will likely offer little
respite in the face of larger
scale climatic changes,
especially as isolated
systems.
Hedgerows do increase
rodent dispersal. These
conservation corridors were
used by small birds but
larger birds prefer flying
from one larger woodlot to
beetle species,
many frogs
Mech and
Hallett, 2001
United States
Local
Mammals:
The red-backed
vole
(Clethrionomys
gapperi) and
the deer mouse
(Peromyscus
maniculatus)
Clear cut and
new growth
forests
Damschen et
al. 2006.
United States
Local
Plants:
long leaf pine
(Pinus
Long leaf pine
Sampling of
(Pinus
patches (Five
palustris) forest years)
34
Genetic
sampling of
10 pairs of
populations
(207
individuals
over 3 years)
3 coniferous
forest systems:
contiguous,
with corridors,
and isolated
patches
Long leaf pine
forest (clear cut
lots)
the next. This is of course
limited by the woodlots’
proximity to one another.
Carabid beetles traveling
across the matrix had a
significantly higher
mortality rate than those
using the hedgerows.
Amphibians use hedgerows
as habitat. It is unclear from
this review how hedgerows
will fare in the face of
climate change, but as
isolated systems they are
weak.
Corridors do help increase
gene flow for red-backed
voles (Clethrionomys
gapperi) because they are
habitat specialists. In the
case of the deer mouse
(Peromyscus maniculatus),
they were able to live and
move across the matrix and
so there was no significant
genetic difference in the
three landscape types. This
study shows that local
corridors will play an
important role in
preventing the extirpation
of habitat specialists by
allowing them to migrate to
more suitable habitat in the
face of climate change.
Their study strongly
supports the use of
conservation corridors to
palustris)
Killeen and
Solorzano,
2008
Amazonia
Regional
Lees and
Peres 2007
Brazil (Amazonia)
Regional
Yellowstoneto-Yukon
Canada and the
United States
Continental
N/A
They examine
the
precipitation
regime.
(N/A)
Birds,
mammals: for
example, the
red-bellied
macaw, spider
monkey
Pastoral and
arable lands
Simulations
Woodlot and
corridor
networks,
including
buffer zones
Pastoral and
arable lands
Sampling to
determine
minimum
optimal
width (37
sites)
riparian sites in
heterogeneous
forests
Large
mammalian
carnivores and
some
mammals:
grizzly bears
(Ursus arctos
Fragmented
industrialized
land
Initially, a
radiocollared gray
wolf (two
years)
Mountain
ecosystem of
1.2 million
square
kilometers
35
enhance species richness
and therefore improve
habitat quality. Connected
cleared patches had 20%
more species richness than
the isolated patches.
Improved habitat quality
protects microhabitats for
use as species adapt to
climate change.
Corridors help maintain
forest land cover and in
turn can help regulate
changing regional
precipitation patterns.
This study shows that
corridor width is a strong
predictor of its success in
mitigating loss of
biodiversity in the face of
climate change. A riparian
corridor of 400 meters in
width is the minimum
appropriate width which
prevents overcrowding,
mitigates edge effects, and
preserves a full range of
microhabitats to allow for
migration with climatic
changes.
This is the best scale at
which conservation
corridors can mitigate the
impact of climate change
because they provide space
for species to migrate and
adapt, especially along
Pulsford et al.
2003
Australia
Continental
horribilis),
gray wolves
(Canis lupus),
NorthAmerican red
squirrel
(Tamiasciurus
hudsonicus)
and pikas
(Ochatona
princeps)
Plant:
The eucalypt
[Eucalyptus
sp.]
altitudinal gradients. They
also protect the large
habitat home range of top
carnivores, thereby
maintaining the integrity of
trophic systems.
Maintaining this forested
mountain land cover also
strongly regulates climate.
Fragmented
industrial land
36
Simulations
Moist eucalypt
forest
This conservation corridor
would connect coastal and
alpine habitat, providing a
stronger network for the
preservation of moist
eucalypt forest and its
reliant biodiversity.
10.0
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